Gamma - ray tomography in fluidised beds using a gamma camera

This paper describes the design and the optimisation of a gamma-ray tomography tool to be used for the measure ment of the particle density in fluidised beds. The set-up consists of a radioactive line source (35 cm long) perpendicular to the axis of the bed (15 cm diameter) and a standard medical gamma camera equipped with a lead collimator (~ 0.02 rad acceptance angle). An optimum gamma-ray energy of ~ 200 keV is deduced. It is shown that no corrections for imperfect collimation are necessary given the small acceptance angle of the collimator. It is estimated that the density profile can be obtained with an absolute accuracy of ± 25 kg/m3 and a spatial resolution of 2.5 mm. The maximum source strength is limited by the maximum count rate of the gamma camera. With a ⁷⁵Se source of 130 mCi the measuring time for a density profile under the assumption of cylinder symmetry is in the order of 150 s.